The present invention is related to the field of printed circuit board fabrication and especially to the field of fabrication of double sided printed circuit boards.
PCT patent publication WO 00/02424, the disclosure of which is incorporated herein by reference, describes a scanning laser direct imaging (LDI) system for writing an electric circuit pattern on a printed circuit board substrate.
FIG. 1 is a reproduction of FIG. 1 of the above referenced publication. Some details of its operation are given below. Further details of the operation and an explanation of the figure can be found in the publication. In such systems, a laser beam or beams, modulated with pattern data, is scanned across a sensitized printed circuit board substrate 78 to write a latent image of a desired electrical circuit pattern.
The substrate is optionally inverted and a second pattern in side to side alignment with the first pattern is written on the other side of the substrate. In accordance with some printed circuit board fabrication techniques, substrate layers may be sequentially laminated to previously produced substrate layers and an electrical circuit pattern is written on the outermost side of each sequentially added layer in a build up fashion. The latent patterns are developed to form etching masks on the substrate. The masked substrate is etched to form the desired electrical circuit pattern.
Among the problems which arise in printed circuit board fabrication is the side to side alignment of printed circuit patterns on various substrate layers, and mutual alignment among patterns printed on various substrate layers. One method utilized to obtain suitable alignment is disclosed in the embodiment of FIGS. 1, 2, 14, 15 and 16, of the publication (FIG. 2 is a reproduction of FIG. 14 of the above referenced publication.). PC board substrate 78 is formed with a plurality of holes 150 at least some of which are preferably aligned, at least roughly, in the scan direction. A base on which the substrate is mounted is formed with openings larger than the holes in the substrate and the holes in the substrate are positioned generally in correspondence to the openings in the base. One or more detectors 152 are positioned below the scan line of the scanner.
As the printed circuit board is transported past the scan line, the scanner scans across the holes in a substrate layer. Based on signals detected by detector 150 via the holes and the openings, the locations of the holes in the substrate layer with respect to the scanner are detected. The base is optionally rotated and scanning of the printed circuit board substrate then commences with the position of the scanning lines pattern being referenced to the location of the holes.
It should be noted that the position of the scanning beam that passes through holes 150 is scanned together with another beam that impinges a scale 80 that is used to determine the true instantaneous (scan dimension) position of the beam in the scan direction. Furthermore, the relative cross-scan position of the holes (and thus the board) is determined utilizing a second scale, typically operatively associated with the base.
When scanning the second side of the substrate, the procedure is repeated to determine the position of the holes and thus the position of the already scanned pattern on the first side of the substrate (or the position of already scanned patterns on lower layers in a build up board) with respect to the coordinate space of the LDI system. This allows for the data in the scanning of each subsequent side to be aligned with respect to previously scanned sides.
Optionally, an additional series of holes in the board and pins on the base, or a guide rail along the base, may be used for rough alignment of the substrate. Such pins are shown in FIG. 16 of the reference. In some conventional systems, only such mechanical means are used for aligning the patterns on the two sides of the substrate. The system may include means for rotating the board to improve alignment.
Measuring systems employing imagers, and especially CCD cameras, are known in the art for use in determining the positioning of a PC board in an LDI scanner. Generally, such cameras may be used to detect various markings on a printed circuit board laminate layer, or to detect an edge of a printed circuit board laminate layer and to relate the detected position of the marking or the edge with a scanner position.
An aspect of some embodiments of the invention is concerned with alignment of the images written on two sides of a PC board.
In exemplary embodiments of the invention, no holes need be made in the printed circuit board in order to provide alignment of the images on both sides.
In some embodiments of the invention, an alignment pattern is written on a first side of the board while an image is written on another side with a scanner in predetermined orientation in relation to the alignment pattern. The scanner used to write the image is provided with at least one detector which can detect the position of the alignment pattern, when the PC board is flipped over. The position of the detector or detectors with respect to the scanner beam is precalibrated relative to the scanner, so that knowledge of the location of the alignment pattern defines the position of the already written image (on the first side now facing away from the scanner) with respect to the scanning system. The at least one detector can be, for example, at least one camera which views the alignment pattern when the PC board is flipped over. This allows for the alignment of the image to be written on the second side with that already written on the first side.
Optionally, the cameras are mounted on a calibrated rail system that allows for at least limited motion of the cameras in the cross scan direction. This allows the at least one camera to move so that it can image the alignment pattern. The provision of this motion is desirable (but not always required) to accommodate the inexact positioning of the PC board when it is flipped over.
Alternatively or additionally, the scanner is equipped with at least one additional camera or other imager, that can view the alignment pattern before flipping the PC board. Such a system is described in Applicant""s copending U.S. patent application Ser. No. 09/708,160 filed Nov. 8, 2000, the disclosure of which is incorporated herein by reference. This document describes a system by which an alignment pattern, such as that described above, is imaged and the location of the scanned image is determined with respect to the camera system. Use of such a system helps to calibrate the locations of images determined by the cameras that view the flip side of the PC board with the scanner.
Alternatively or additionally, the positional relationship between the cameras that view the two sides of the PC board is determined by providing a substrate with holes that can be imaged from both sides of the board. This allows for the determination of a transformation between the coordinate systems of the cameras that view both sides. One non-limiting method for accurate determination of the positions of the holes in the coordinate systems is described, for example in PCT publication WO 00/02424, the disclosure of which is incorporated herein by reference.
In other embodiments of the invention, an alignment pattern is written on the second side of the board at the same time as the scanner image is being written on the first side of the board. This pattern can be provided by a fixed or movable source, for example a light source that writes a reticule on the second side. This alignment pattern is thus in alignment with the image written on the first side. When the PC board is turned over, the alignment pattern is imaged by at least one detector (such as at least one camera) that views the same side of the board that is available for scanning (writing) by the scanner. The scanner is pre-calibrated with the cameras (for example utilizing one of the methods described in the above referenced U.S. Ser. No. 09/708,160, so that determining the location of the alignment pattern allows for the writing of the image on the second side in alignment with that written on the first side.
The source may be fixed or, alternatively, may include a light guide, which provides light along a substantial extent in the cross-scan direction. A master plate with a pattern of holes may be provided between the guide and the underside of the PC board, such that the hole pattern is written on the second side of the board. This pattern may be varied to suit the extent of the board.
It should be understood that there are three different elements, in three coordinate systems, which must be referenced to each other. On of these is the scanner and its associated reference system. The second is the cameras and their associated reference system. The third is the alignment pattern writer on the reverse side of the board, which is not in either coordinate system. Exemplary, non-limiting methods for deriving a transformation between the coordinate systems of the scanner and the cameras are given in the above referenced U.S. Ser. No. 09/708,160. Other suitable methods can also be used.
The alignment pattern writer can be referenced to the cameras in a number of ways. One exemplary way is to provide a ground glass at the position of the back of the PC and to image the pattern with the cameras. Thus, the position of the patterns in the camera coordinates can be determined. Then, when an image is written by the scanner and a simultaneous alignment pattern is written on the reverse side, the relationship between the two may be easily determined. Alternatively, the pattern may be directly imaged without the presence of a ground glass. Imaging of the alignment pattern, by the cameras, after turning over the PC board, allows for the positioning of the new image written by the scanner referenced to the image on the first side.
There is thus provided, in accordance with an exemplary embodiment of the invention, a method of recording aligned images on two sides of a printed circuit board substrate, comprising:
recording an image of an electrical circuit pattern on a first side of a printed circuit board substrate;
forming an alignment pattern on a side of the printed circuit board substrate, wherein said alignment pattern has a known spatial relationship to said image of an electrical circuit pattern;
determining a location of the alignment pattern on the printed circuit board substrate; and
recording an image of an electrical circuit pattern on a second side of the printed circuit board substrate in response to the determined location of the alignment pattern.
Optionally, determining includes imaging the alignment pattern with at least one imager.
Optionally, forming an alignment pattern on a side of the printed circuit board substrate includes forming the alignment pattern on the first side of the printed circuit board substrate. Additionally or alternatively, forming an alignment pattern on a side of the printed circuit board substrate optionally includes forming the alignment pattern on the second side of the printed circuit board substrate. Additionally or alternatively, forming an alignment pattern on a side of the printed circuit board substrate optionally includes forming the alignment pattern at least partially simultaneously while said image of an electrical circuit pattern is being recorded.
In an embodiment of the invention, forming an alignment pattern on a side of the printed circuit board substrate comprises:
providing a photosensitive coating that is formulated to produce a visible image when exposed to light of a predetermined wavelength; and
selectively exposing said photosensitive coating with light of said predetermined wavelength.
Optionally, the photosensitive coating is a photoresist applied to a surface of said printed circuit board substrate. Optionally alternatively or additionally the photosensitive coating is a photosensitive label applied to a surface of said printed circuit board substrate.
Optionally, forming an alignment pattern comprises providing a physical marking on said printed circuit board substrate.
In an embodiment of the invention, selectively exposing comprises selectively exposing using a light source different from a light source used to record said image of an electrical circuit pattern.
Optionally, the light source provides patterned light to said second side of the printed circuit board while the image on the first side is being recorded.
In an embodiment of the invention, selectively exposing comprises selectively exposing said photosensitive coating with light provided by light beam that is employed to record at least part of an electrical circuit image pattern on printed circuit board substrate.
In an embodiment of the invention, selectively exposing comprises exposing said photosensitive surface through a mask.
Optionally, the alignment pattern is formed while the first side is in an orientation in which the image thereon is written.
In an embodiment of the invention, the alignment pattern is formed on said second side.
In an embodiment of the invention, selectively exposing comprises selectively exposing said photosensitive coating with light provided by light beam split off from said light beam that is employed to record at least part of an electrical circuit image pattern on printed circuit board substrate. Optionally, the alignment pattern is formed while the first side is in an orientation in which the image thereon is written. Optionally, the alignment pattern is formed on said second side. Optionally, the alignment pattern is formed simultaneously with the image.
Optionally, the predetermined wavelength is in the UV spectrum.
In an embodiment of the invention, the recording an image of an electrical circuit pattern includes:
providing said printed circuit board substrate coated with a photosensitive coating; and
scanning said printed circuit board substrate coated with a photosensitive coating with a modulated laser beam.
Optionally, determining a location comprises:
determining a relationship between a coordinate system of a system for recording an image of an electrical circuit pattern and a coordinate system of an imager for viewing a side of said printed circuit board substrate board;
determining a location of the alignment pattern in the coordinate system of said imager; and
determining a location of the alignment pattern in the coordinate system of said system for recording an image of an electrical circuit pattern in response to said relationship.
In an embodiment of the invention, determining a location of the alignment pattern formed on the second side of the printed circuit board substrate comprises:
recording a visible alignment pattern on a second side of a substrate;
determining a spatial relationship between said visible alignment pattern and a location addressed by a pattern recording system;
inverting said substrate;
determining a post inversion position of said location addressed by said pattern recording system;
imaging said visible alignment pattern with an imager to determine a post inversion position of said visible alignment pattern;
calculating the position of said alignment pattern in response to indications of said location, said post-inversion position of said location and said post inversion position of said alignment pattern.
Optionally, determining the first spatial relationship comprises determining the location of at least one hole formed in a substrate.
In an embodiment of the invention, the at least one imager comprises a single imager. Alternatively, the at least one imager comprises a plurality of imagers. Optionally, the at least one imager is fixed in position. Alternatively, the at least one imager is moveable and including means for determining its position.
There is further provided, in accordance with an embodiment of the invention, a method for determining a position whereat a pattern is formed on a first side of a substrate relative to a position on a second side of the substrate, comprising:
forming a pattern on a first side of a substrate;
determining a position of at least one location on a substrate when said substrate is in a first spatial orientation at which the pattern is formed on the first side of the substrate;
inverting said substrate;
determining a position of said at least one location when said substrate is inverted:
sensing a position of said pattern when said substrate is inverted; and
calculating the position of said pattern on said first side of said substrate in response to inputs including: the position of said location when said substrate is in said first orientation, the position of said location when said substrate is inverted, and the position of said pattern when said substrate is inverted.
Optionally, said forming includes exposing a pattern in a photosensitive coating disposed on said substrate.
Optionally, the said pattern is visible without developing said photosensitive coating.
In an embodiment of the invention, the location is a hole in said substrate.
There is further provided, in accordance with an embodiment of the invention, a method according to claim 32 wherein said determining a position of said at least one location includes
addressing said location with a beam of light;
sensing the presence of the beam of light at said address; and
determining the position of the beam of light at said address.
Optionally, sensing includes imaging said pattern with an imager.
There is further provided, in accordance with an embodiment of the invention, apparatus for forming an images on first and second sides of a printed circuit board substrate, comprising:
a scanner adapted to form a first image of an electrical circuit pattern on a first side of the substrate when the substrate is placed thereon in a first orientation;
means for forming an alignment pattern on the first side or the second side, said alignment pattern having a known spatial relationship to said electrical circuit pattern;
an imager that views the alignment pattern when the substrate is inverted and generates an alignment pattern image information; and
a controller that receives the alignment pattern image information and controls the scanner to form a second image on the second side, said second image being aligned with said first image, by the controller, responsive to the alignment pattern image information.
Optionally, the imager views the first side of the substrate when the substrate is in the first orientation. Optionally, the alignment pattern is formed on the second side of the substrate, when the substrate is in the first orientation. Optionally, the apparatus includes an optical system that directs light from the scanner to the second side to form the alignment pattern.
Optionally, the apparatus includes a source of radiation positioned and operative to irradiate the second side with patterned light.
Optionally, the imager views the second side of the substrate when the substrate is in the first position. Optionally, the alignment pattern is written on the first side of the substrate, when the substrate is in the first orientation. Optionally, the controller controls the scanner to write the alignment pattern on the first side.
In some embodiments, the apparatus includes a memory in which a relationship between a coordinate system of the imager and a coordinate system of the scanner is recorded, said relationship being utilized by the controller to control the alignment of the second image.
In some embodiments, the apparatus includes a memory in which a spatial relationship between the patterned light generator and the coordinate system of the imager is recorded, said relationship being utilized by the controller to control the alignment of the second image.
In some embodiments, the apparatus includes a memory in which a spatial relationship between the patterned light generator and the coordinate system of the scanner is recorded, said relationship being utilized by the controller to control the alignment of the second image.
There is further provided a method for forming an images on first and second sides of a printed circuit board substrate, comprising:
recording a first image of an electrical circuit pattern on a first side of the substrate, by scanning, when the substrate is in a first orientation;
forming an alignment pattern on the first side or the second side, said alignment pattern having a known spatial relationship to said electrical circuit pattern;
inverting the substrate;
imaging the alignment pattern when the substrate is inverted and generating alignment pattern image information;
determining a position and orientation for scanning a pattern to record a second electrical circuit pattern on the second side, at which the position and orientation the first and second electric circuit patterns are aligned, responsive to the known spatial relationship and the alignment pattern information;
recording a second image of an electrical circuit pattern on the second side, by scanning, responsive to said determination.